Resist composition and patterning process

ABSTRACT

A resist composition comprising an alkali metal salt of tetraiodophenolphthalein, tetraiodophenolsulfonphthalein or tetraiodofluorescein exhibits a sensitizing effect and an acid diffusion suppressing effect and forms a pattern having improved resolution, LWR and CDU.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2016-182952 filed in Japan on Sep. 20,2016, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a resist composition comprising an alkalimetal salt of tetraiodophenolphthalein, tetraiodophenolsulfonphthalein,tetraiodofluorescein or a derivative thereof, and a patterning processusing the same.

BACKGROUND ART

To meet the demand for higher integration density and operating speed ofLSIs, the effort to reduce the pattern rule is in rapid progress. Thewide-spreading flash memory market and the demand for increased storagecapacities drive forward the miniaturization technology. As the advancedminiaturization technology, manufacturing of microelectronic devices atthe 65-nm node by the ArF lithography has been implemented in a massscale. Manufacturing of 45-nm node devices by the next generation ArFimmersion lithography is approaching to the verge of high-volumeapplication. The candidates for the next generation 32-nm node includeultra-high NA lens immersion lithography using a liquid having a higherrefractive index than water in combination with a high refractive indexlens and a high refractive index resist film, EUV lithography of 13.5 nmwavelength, and double patterning version of the ArF lithography, onwhich active research efforts have been made.

The exposure system for mask manufacturing made a transition from thelaser beam exposure system to the EB exposure system to increase theaccuracy of line width. Since a further size reduction becomes possibleby increasing the accelerating voltage of the electron gun in the EBexposure system, the accelerating voltage increased from 10 kV to 30 kVand reached 50 kV in the current mainstream system, with a voltage of100 kV being under investigation.

As the pattern feature size is reduced, approaching to the diffractionlimit of light, light contrast lowers. In the case of positive resistfilm, a lowering of light contrast leads to reductions of resolution andfocus margin of hole and trench patterns.

As the pattern feature size is reduced, the edge roughness (LWR) of linepatterns and the critical dimension uniformity (CDU) of hole patternsare regarded significant. It is pointed out that these factors areaffected by the segregation or agglomeration of a base polymer and acidgenerator and the diffusion of generated acid. There is a tendency thatas the resist film becomes thinner, LWR becomes greater. A filmthickness reduction to comply with the progress of size reduction causesa degradation of LWR, which becomes a serious problem.

The EUV lithography resist must meet high sensitivity, high resolutionand low LWR at the same time. As the acid diffusion distance is reduced,LWR is reduced, but sensitivity becomes lower. For example, as the PEBtemperature is lowered, the outcome is a reduced LWR, but a lowersensitivity. As the amount of quencher added is increased, the outcomeis a reduced LWR, but a lower sensitivity. It is necessary to overcomethe tradeoff relation between sensitivity and LWR. It would be desirableto have a resist material having a high sensitivity and resolution aswell as improved LWR and CDU.

Phenolphthalein opens its ring in alkaline water to generate a carboxylgroup to thereby increase an alkaline dissolution rate. Utilizing thismechanism, Patent Document 1 proposes a positive resist compositioncomprising phenolphthalein. Patent Document 2 proposes a positive resistcomposition comprising phenolphthalein whose phenolic hydroxyl group issubstituted with an acid labile group.

Patent Document 3 proposes a chemically amplified resist compositioncomprising a metal salt of carboxylic acid. The metal salt of carboxylicacid undergoes anion exchange with fluorosulfonic acid generated by anacid generator upon light exposure. That is, from the metal salt ofcarboxylic acid and fluorosulfonic acid, a metal salt of fluorosulfonicacid is formed and carboxylic acid is released. Since the metal salt offluorosulfonic acid is neutral, it does not provoke deprotectionreaction. This means that the metal salt of carboxylic acid functions asa quencher for fluorosulfonic acid. Since the metal has a highermolecular weight than hydrocarbons and is more effective for suppressingacid diffusion, the metal salt functions as an improved quencher.

CITATION LIST

Patent Document 1: JP-A 2005-338481

Patent Document 2: JP-A H05-313371 (U.S. Pat. No. 5,348,838)

Patent Document 3: JP-A 2013-025211 (U.S. Pat. No. 9,360,753)

SUMMARY OF INVENTION

As the wavelength of light becomes shorter, the energy density thereofbecomes higher and hence, the number of photons generated upon exposurebecomes smaller. A variation in photon number causes variations in LWRand CDU. As the exposure dose increases, the number of photonsincreases, leading to a less variation of photon number. Thus there is atradeoff relationship between sensitivity and resolution, LWR and CDU.In particular, the EUV lithography resist materials have the tendencythat a lower sensitivity leads to better LWR and CDU.

An increase in acid diffusion also causes degradation of resolution, LWRand CDU. This is because acid diffusion not only causes image blur, butalso proceeds non-uniformly in a resist film. For suppressing aciddiffusion, it is effective to lower the PEB temperature, to use a bulkyacid which is least diffusive, or to increase the amount of quencheradded. However, any of these means for reducing acid diffusion resultsin a lowering of sensitivity. Either the means for reducing photonvariation or the means for reducing acid diffusion variation leads to alowering of resist sensitivity.

An object of the invention is to provide a resist composition whichexerts a high sensitizing effect and an acid diffusion suppressingeffect and has improved resolution, LWR and CDU, and a pattern formingprocess using the same.

A significant increase of acid generation efficiency and a significantsuppression of acid diffusion must be achieved before the tradeoffrelationship between sensitivity and resolution, LWR and CDU can beovercome.

Tetraiodophenolphthalein, tetraiodophenolsulfonphthalein andtetraiodofluorescein have four iodine atoms in their molecule. Iodine issubstantially absorptive to EUV of wavelength 13.5 nm and EB because ofits high atomic number, and releases many secondary electrons uponexposure because of many electron orbits in its molecule. The secondaryelectrons thus released provide energy transfer to an acid generator,achieving a high sensitizing effect. However, sincetetraiodophenolphthalein, tetraiodophenolsulfonphthalein andtetraiodofluorescein are substantially ineffective for suppressing aciddiffusion and fully alkaline soluble, a resist material having any ofthese added thereto forms a fine size pattern which suffers a filmthickness loss of lines.

The inventor has found that when a salt of tetraiodophenolphthalein,tetraiodophenolsulfonphthalein or tetraiodofluorescein neutralized withan alkali metal is added to a base polymer, the resulting resistcomposition forms a resist film which exerts a high sensitizing effectand an acid diffusion suppressing effect and has a high sensitivity,minimized LWR and improved CDU.

In one aspect, the invention provides a resist composition comprising abase polymer and an alkali metal salt of a compound selected from thegroup consisting of tetraiodophenolphthalein,tetraiodophenolsulfonphthalein, tetraiodofluorescein, and derivativesthereof.

Typically, the alkali metal salt has the formula (A)-1 or (A)-2.

Herein R¹ and R² are hydrogen, or R¹ and R² may bond together to form anether group, R³ is hydrogen, halogen, hydroxyl or C₁-C₄ alkoxy group, Gis carbonyl or sulfonyl, and A⁺ is an alkali metal ion selected from thegroup consisting of sodium, potassium, rubidium, and cesium ions.

The resist composition may further comprise an acid generator capable ofgenerating sulfonic acid, sulfonimide or sulfonmethide.

The resist composition may further comprise an organic solvent.

In a preferred embodiment, the base polymer comprises recurring unitshaving the formula (a1) or recurring units having the formula (a2).

Herein R^(A) is each independently hydrogen or methyl, R¹¹ and R¹² areeach independently an acid labile group, X is a single bond, phenylene,naphthylene, or a C₁-C₁₂ linking group containing ester moiety orlactone ring, and Y is a single bond or ester group.

The resist composition may further comprise a dissolution inhibitor.

In one embodiment, the resist composition is a chemically amplifiedpositive resist composition.

In another embodiment, the base polymer is an acid labile group-freepolymer.

The resist composition may further comprise a crosslinker. Then theresist composition is a chemically amplified negative resistcomposition.

In one preferred embodiment, the base polymer comprises recurring unitsof at least one type selected from recurring units having the formulae(f1) to (f3).

Herein R^(A) is each independently hydrogen or methyl. Z¹ is a singlebond, phenylene, —O—Z¹¹—, or —C(═O)—Z¹²—Z¹¹—, Z¹¹ is a straight,branched or cyclic C₁-C₆ alkylene group or straight, branched or cyclicC₂-C₆ alkenylene group which may contain a carbonyl, ester, ether orhydroxyl moiety, or phenylene group, Z¹² is —O— or —NH—. R²¹, R²², R²³,R²⁴, R²⁵, R²⁶, R²⁷, and R²⁸ are each independently a straight, branchedor cyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester orether moiety, or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or mercaptophenyl group.Z² is a single bond, —Z²¹—C(═O)—O—, —Z²¹—O—, or —Z²¹—O—C(═O)—, Z²¹ is astraight, branched or cyclic C₁-C₁₂ alkylene group which may contain acarbonyl, ester or ether moiety. Z³ is a single bond, methylene,ethylene, phenylene, fluorinated phenylene, —O—Z³¹—, or —C(═O)—Z³²—Z³¹—,Z³¹ is a straight, branched or cyclic C₁-C₆ alkylene group or straight,branched or cyclic C₂-C₆ alkenylene group which may contain a carbonyl,ester, ether or hydroxyl moiety, or a phenylene, fluorinated phenyleneor trifluoromethyl-substituted phenylene group, Z³² is —O— or —NH—. A¹is hydrogen or trifluoromethyl, and M⁻ is a non-nucleophilic counterion.

The resist composition may further comprise a surfactant.

In another aspect, the invention provides a pattern forming processcomprising the steps of coating the resist composition defined aboveonto a substrate, baking, exposing the resulting resist film tohigh-energy radiation, and developing with a developer.

Typically, the high-energy radiation is ArF excimer laser of wavelength193 nm, KrF excimer laser of wavelength 248 nm, EB or EUV of wavelength3 to 15 nm.

Advantageous Effects of Invention

Because of a high content of iodine featuring substantial lightabsorption, a resist film containing an alkali metal salt oftetraiodophenolphthalein, tetraiodophenolsulfonphthalein,tetraiodofluorescein or a derivative thereof exhibits a sensitizingeffect due to secondary electrons released therefrom upon exposure, anacid diffusion suppressing effect, and a high dissolution contrast. Thusthe resist film exhibits high resolution and minimal LWR as a positiveor negative resist film subject to alkaline development or as a negativeresist film subject to organic solvent development.

DESCRIPTION OF EMBODIMENTS

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. The notation(C_(n)-C_(m)) means a group containing from n to m carbon atoms pergroup. Me stands for methyl, Ac for acetyl, and Ph for phenyl.

The abbreviations and acronyms have the following meaning.

EB: electron beam

EUV: extreme ultraviolet

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight distribution or dispersity

GPC: gel permeation chromatography

PEB: post-exposure bake

PAG: photoacid generator

LWR: line width roughness

CDU: critical dimension uniformity

Resist Composition

The resist composition of the invention is defined as comprising a basepolymer and an alkali metal salt of a compound selected from the groupconsisting of tetraiodophenolphthalein, tetraiodophenolsulfonphthalein,tetraiodofluorescein, and derivatives thereof. The alkali metal salt oftetraiodophenolphthalein, tetraiodophenolsulfonphthalein,tetraiodofluorescein or derivative thereof is sometimes referred to as“phthalein alkali metal salt” for simplicity sake. The phthalein alkalimetal salt undergoes ion exchange with sulfonic acid, sulfonimide orsulfonmethide generated from an acid generator, especially sulfonic acidcontaining fluorinated alkyl, bissulfonimide or trissulfonmethide, toform a salt and release tetraiodophenolphthalein,tetraiodophenolsulfonphthalein or tetraiodofluorescein. The alkali metalhas an acid trapping ability and an acid diffusion suppressing effect.Since the phthalein alkali metal salt is not photosensitive and thus notphoto-decomposable, it retains a sufficient acid trapping ability evenin the unexposed region, suppressing acid diffusion from the exposedregion to the unexposed region.

Besides the phthalein alkali metal salt, another amine compound,ammonium salt, sulfonium salt or iodonium salt may be separately addedas the quencher to the resist composition of the invention. The ammoniumsalt, sulfonium salt or iodonium salt added as quencher is preferably asulfonium salt or iodonium salt of carboxylic acid, sulfonic acid,sulfonamide or saccharin. The carboxylic acid may or may not befluorinated at α-position.

The acid diffusion suppressing effect and contrast enhancing effect ofthe phthalein alkali metal salt are valid in both the positive ornegative pattern formation by alkaline development and the negativepattern formation by organic solvent development.

Phthalein Alkali Metal Salt

The phthalein alkali metal salt in the resist composition is an alkalimetal salt of a compound selected from among tetraiodophenolphthalein,tetraiodophenolsulfonphthalein, tetraiodofluorescein, and derivativesthereof. Typically the phthalein alkali metal salt has the formula (A)-1or (A)-2.

Herein R¹ and R² are hydrogen, or R¹ and R² may bond together to form anether group. R³ is hydrogen, halogen, hydroxyl or C₁-C₄ alkoxy group. Gis carbonyl or sulfonyl. A⁺ is an alkali metal ion selected from amongsodium, potassium, rubidium, and cesium ions or a mixture thereof.

Examples of the phthalein alkali metal salt of formula (A)-1 or (A)-2are given below, but not limited thereto. Herein A⁺ is as defined above.

Since the phthalein alkali metal salt contains four iodine atoms in themolecule, it has substantial EUV absorption. Upon EUV exposure, itgenerates secondary electrons, followed by energy transfer to an acidgenerator, leading to sensitization.

Tetraiodophenolphthalein, tetraiodophenolsulfonphthalein ortetraiodofluorescein, in which a phenolic hydroxyl group is flanked withiodine atoms as electron-withdrawing group, has a high acidity and ahigh alkali development rate. For this reason, a resist film containingthe phthalein compound undergoes a film thickness loss of pattern linesafter alkaline development. Since the phthalein compound lacks an aciddiffusion suppressing effect, substantial acid diffusion takes place,resulting in degradation of resolution, LWR and CDU.

In contrast, since the phthalein alkali metal salt has been neutralizedwith the alkali metal, its alkali dissolution rate is not so high. Thena resist film containing the phthalein alkali metal salt undergoes nofilm thickness loss of pattern lines after alkaline development. Thealkali metal has a very high ability of neutralizing the acid generatedby an acid generator, does not allow the once neutralized acid todiffuse because of its high molecular weight, and has a high aciddiffusion controlling ability. Among the alkali metals, cesium havingthe highest molecular weight has the highest acid diffusion suppressingeffect, and the effect decreases in the order of rubidium, potassium andsodium.

The phthalein alkali metal salt may be readily prepared, for example, bymixing tetraiodophenolphthalein, tetraiodophenolsulfonphthalein ortetraiodofluorescein with a hydroxide or carbonate of an alkali metal.

In view of sensitivity and acid diffusion suppressing effect, thephthalein alkali metal salt is preferably present in the resistcomposition in an amount of 0.001 to 50 parts, more preferably 0.01 to20 parts by weight per 100 parts by weight of the base polymer to bedescribed below.

Base Polymer

In the case of a positive resist composition, the base polymer in theresist composition is a polymer comprising acid labile group-containingrecurring units. The acid labile group-containing recurring units arepreferably recurring units having the formula (a1) or recurring unitshaving the formula (a2). Sometimes these recurring units are simplyreferred to as recurring units (a1) and (a2).

Herein R^(A) is each independently hydrogen or methyl. R¹¹ and R¹² areeach independently an acid labile group. X is a single bond, phenylene,naphthylene, or a C₁-C₁₂ linking group containing ester moiety orlactone ring. Y is a single bond or ester group.

Examples of the recurring units (a1) are shown below, but not limitedthereto. Herein R^(A) and R¹¹ are as defined above.

The acid labile groups represented by R¹¹ and R¹² in the recurring units(a1) and (a2) may be selected from a variety of such groups, forexample, those groups described in JP-A 2013-080033 (U.S. Pat. No.8,574,817) and JP-A 2013-083821 (U.S. Pat. No. 8,846,303).

Typical of the acid labile group are groups of the following formulae(AL-1) to (AL-3).

In formulae (AL-1) and (AL-2), R¹³ and R¹⁶ are each independently amonovalent hydrocarbon group of 1 to 40 carbon atoms, preferably 1 to 20carbon atoms, typically straight, branched or cyclic alkyl, which maycontain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. R¹⁴and R¹⁵ are each independently hydrogen or a monovalent hydrocarbongroup of 1 to 20 carbon atoms, typically straight, branched or cyclicalkyl, which may contain a heteroatom such as oxygen, sulfur, nitrogenor fluorine. A1 is an integer of 0 to 10, especially 1 to 5. A pair ofR¹⁴ and R¹⁵, R¹⁴ and R¹⁶, or R¹⁵ and R¹⁶ may bond together to form aring, typically alicyclic, with the carbon atom or carbon and oxygenatoms to which they are attached, the ring containing 3 to 20 carbonatoms, preferably 4 to 16 carbon atoms.

In formula (AL-3), R¹⁷, R¹⁸ and R¹⁹ are each independently a monovalenthydrocarbon group of 1 to 20 carbon atoms, typically straight, branchedor cyclic alkyl, which may contain a heteroatom such as oxygen, sulfur,nitrogen or fluorine. A pair of R¹⁷ and R¹⁸, R¹⁷ and R¹⁹, or R¹⁸ and R¹⁹may bond together to form a ring, typically alicyclic, with the carbonatom to which they are attached, the ring containing 3 to 20 carbonatoms, preferably 4 to 16 carbon atoms.

The base polymer may further comprise recurring units (b) having aphenolic hydroxyl group as an adhesive group. Examples of suitablemonomers from which recurring units (b) are derived are given below, butnot limited thereto. Herein R^(A) is as defined above.

Further, recurring units (c) having another adhesive group selected fromhydroxyl (other than the foregoing phenolic hydroxyl), lactone ring,ether, ester, carbonyl and cyano groups may also be incorporated in thebase polymer. Examples of suitable monomers from which recurring units(c) are derived are given below, but not limited thereto. Herein R^(A)is as defined above.

In the case of a monomer having a hydroxyl group, the hydroxyl group maybe replaced by an acetal group susceptible to deprotection with acid,typically ethoxyethoxy, prior to polymerization, and the polymerizationbe followed by deprotection with weak acid and water. Alternatively, thehydroxyl group may be replaced by an acetyl, formyl, pivaloyl or similargroup prior to polymerization, and the polymerization be followed byalkaline hydrolysis.

In another preferred embodiment, the base polymer may further compriserecurring units (d) selected from units of indene, benzofuran,benzothiophene, acenaphthylene, chromone, coumarin, and norbornadiene,or derivatives thereof. Suitable monomers are exemplified below.

Besides the recurring units described above, further recurring units (e)may be incorporated in the base polymer, examples of which includestyrene, vinylnaphthalene, vinylanthracene, vinylpyrene,methyleneindene, vinylpyridine, and vinylcarbazole.

In a further embodiment, recurring units (f) derived from an onium salthaving a polymerizable carbon-carbon double bond may be incorporated inthe base polymer. JP-A 2005-084365 discloses sulfonium and iodoniumsalts having a polymerizable carbon-carbon double bond capable ofgenerating a sulfonic acid. JP-A 2006-178317 discloses a sulfonium salthaving sulfonic acid directly attached to the main chain.

The preferred recurring units (f) include recurring units having formula(f1), recurring units having formula (f2), and recurring units havingformula (f3). These units are simply referred to as recurring units(f1), (f2) and (f3), which may be used alone or in combination of two ormore types.

Herein R^(A) is each independently hydrogen or methyl. Z¹ is a singlebond, phenylene, —O—Z¹¹—, or —C(═O)—Z¹²—Z¹¹—, wherein Z¹¹ is a straight,branched or cyclic C₁-C₆ alkylene group or straight, branched or cyclicC₂-C₆ alkenylene group which may contain a carbonyl, ester, ether orhydroxyl moiety, or phenylene group, Z¹² is —O— or —NH—. R²¹, R²², R²³,R²⁴, R²⁵, R²⁶, R²⁷, and R²⁸ are each independently a straight, branchedor cyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester orether moiety, or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or mercaptophenyl group.Z² is a single bond, —Z²¹—C(═O)—O—, —Z²¹—O—, or —Z²¹—O—C(═O)—, whereinZ²¹ is a straight, branched or cyclic C₁-C₁₂ alkylene group which maycontain a carbonyl, ester or ether moiety. Z³ is a single bond,methylene, ethylene, phenylene, fluorinated phenylene, —O—Z³¹—, or—C(═O)—Z³²—Z³¹—, wherein Z³¹ is a straight, branched or cyclic C₁-C₆alkylene group or straight, branched or cyclic C₂-C₆ alkenylene groupwhich may contain a carbonyl, ester, ether or hydroxyl moiety, or aphenylene, fluorinated phenylene or trifluoromethyl-substitutedphenylene group, Z³² is —O— or —NH—. A¹ is hydrogen or trifluoromethyl.M⁻ is a non-nucleophilic counter ion.

Examples of the monomer from which recurring unit (f1) is derived areshown below, but not limited thereto. R^(A) and M⁻ are as defined above.

Examples of the non-nucleophilic counter ion M⁻ include halide ions suchas chloride and bromide ions; fluoroalkylsulfonate ions such astriflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate;arylsulfonate ions such as tosylate, benzenesulfonate,4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate;alkylsulfonate ions such as mesylate and butanesulfonate; sulfonimidessuch as bis(trifluoromethylsulfonyl)imide,bis(perfluoroethylsulfonyl)imide and bis(perfluorobutylsulfonyl)imide;sulfonmethides such as tris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide.

Also included are sulfonates having fluorine substituted at α-positionas represented by the formula (K-1) and sulfonates having fluorinesubstituted at α- and β-positions as represented by the formula (K-2).

In formula (K-1), R³¹ is hydrogen, or a C₁-C₂₀ straight, branched orcyclic alkyl group, C₂-C₂₀ straight, branched or cyclic alkenyl group,or C₆-C₂₀ aryl group, which may contain an ether, ester, carbonylmoiety, lactone ring, or fluorine atom. In formula (K-2), R³² ishydrogen, or a C₁-C₃₀ straight, branched or cyclic alkyl group, C₂-C₃₀straight, branched or cyclic acyl group, C₂-C₂₀ straight, branched orcyclic alkenyl group, C₆-C₂₀ aryl group or C₆-C₂₀ aryloxy group, whichmay contain an ether, ester, carbonyl moiety or lactone ring.

Examples of the monomer from which recurring unit (f2) is derived areshown below, but not limited thereto. R^(A) is as defined above.

Examples of the monomer from which recurring unit (f3) is derived areshown below, but not limited thereto. R^(A) is as defined above.

The attachment of an acid generator to the polymer main chain iseffective in restraining acid diffusion, thereby preventing a reductionof resolution due to blur by acid diffusion. Also edge roughness isimproved since the acid generator is uniformly distributed.

The base polymer for formulating the positive resist compositioncomprises recurring units (a1) or (a2) having an acid labile group asessential component and additional recurring units (b), (c), (d), (e),and (f) as optional components. A fraction of units (a1), (a2), (b),(c), (d), (e), and (f) is: preferably 0≤a1<1.0, 0≤a2<1.0, 0<a1+a2<1.0,0≤b≤0.9, 0≤c≤0.9, 0≤d≤0.8, 0≤e≤0.8, and 0≤f≤0.5; more preferably0≤a1≤0.9, 0≤a2≤0.9, 0.1≤a1+a2≤0.9, 0≤b≤0.8, 0≤c≤0.8, 0≤d≤0.7, 0≤e≤0.7,and 0≤f≤0.4; and even more preferably 0≤a1≤0.8, 0≤a2≤0.8, 0.1≤a1+a2≤0.8,0≤b≤0.75, 0≤c≤0.75, 0≤d≤0.6, 0≤e≤0.6, and 0≤f≤0.3. Notably, f=f1+f2+f3,meaning that unit (f) is at least one of units (f1) to (f3), anda1+a2+b+c+d+e+f=1.0.

For the base polymer for formulating the negative resist composition, anacid labile group is not necessarily essential. The base polymercomprises recurring units (b), and optionally recurring units (c), (d),(e), and/or (f). A fraction of these units is: preferably 0<b≤1.0,0≤c≤0.9, 0≤d≤0.8, 0≤e≤0.8, and 0≤f≤0.5; more preferably 0.2≤b≤1.0,0≤c≤0.8, 0≤d≤0.7, 0≤e≤0.7, and 0≤f≤0.4; and even more preferably0.3≤b≤1.0, 0≤c≤0.75, 0≤s≤0.6, 0≤e≤0.6, and 0≤f≤0.3. Notably, f=f1+f2+f3,meaning that unit (f) is at least one of units (f1) to (f3), andb+c+d+e+f=1.0.

The base polymer may be synthesized by any desired methods, for example,by dissolving one or more monomers selected from the monomerscorresponding to the foregoing recurring units in an organic solvent,adding a radical polymerization initiator thereto, and effecting heatpolymerization. Examples of the organic solvent which can be used forpolymerization include toluene, benzene, tetrahydrofuran, diethyl ether,and dioxane. Examples of the polymerization initiator used hereininclude 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours.

When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, analternative method is possible. Specifically, acetoxystyrene oracetoxyvinylnaphthalene is used instead of hydroxystyrene orhydroxyvinylnaphthalene, and after polymerization, the acetoxy group isdeprotected by alkaline hydrolysis, for thereby converting the polymerproduct to hydroxystyrene or hydroxyvinylnaphthalene. For alkalinehydrolysis, a base such as aqueous ammonia or triethylamine may be used.Preferably the reaction temperature is −20° C. to 100° C., morepreferably 0° C. to 60° C., and the reaction time is 0.2 to 100 hours,more preferably 0.5 to 20 hours.

The base polymer should preferably have a weight average molecularweight (Mw) in the range of 1,000 to 500,000, and more preferably 2,000to 30,000, as measured by GPC versus polystyrene standards usingtetrahydrofuran (THF) solvent. With too low a Mw, the resist compositionmay become less heat resistant. A polymer with too high a Mw may losealkaline solubility and give rise to a footing phenomenon after patternformation.

If a base polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that foreign matter isleft on the pattern or the pattern profile is degraded. The influencesof molecular weight and dispersity become stronger as the pattern rulebecomes finer. Therefore, the base polymer should preferably have anarrow dispersity (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in orderto provide a resist composition suitable for micropatterning to a smallfeature size.

It is understood that a blend of two or more polymers which differ incompositional ratio, Mw or Mw/Mn is acceptable.

Acid Generator

To the resist composition comprising the phthalein alkali metal salt andthe base polymer, defined above, preferably an acid generator is addedso that the composition may function as a chemically amplified positiveor negative resist composition. The acid generator is typically acompound (PAG) capable of generating an acid upon exposure to actinicray or radiation. Although the PAG used herein may be any compoundcapable of generating an acid upon exposure to high-energy radiation,those compounds capable of generating sulfonic acid, sulfonimide orsulfonmethide are preferred. Suitable PAGs include sulfonium salts,iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, andoxime-O-sulfonate acid generators. Exemplary acid generators aredescribed in JP-A 2008-111103, paragraphs [0122]-[0142] (U.S. Pat. No.7,537,880).

As the PAG, compounds having the formula (1) or (2) are also preferablyused.

In formula (1), R¹⁰¹, R¹⁰² and R¹⁰³ are each independently a straight,branched or cyclic C₁-C₂₀ monovalent hydrocarbon group which may containa heteroatom, any two of R¹⁰¹, R¹⁰² and R¹⁰³ may bond together to form aring with the sulfur atom to which they are attached.

In formula (1), X⁻ is an anion selected from the formulae (1A) to (1D).

In formula (1A), R^(fa) is fluorine or a straight, branched or cyclicC₁-C₄₀ monovalent hydrocarbon group which may contain a heteroatom.

Of the anions of formula (1A), a structure having formula (1A′) ispreferred.

In formula (1A′), R¹⁰⁴ is hydrogen or trifluoromethyl, preferablytrifluoromethyl. R¹⁰⁵ is a straight, branched or cyclic C₁-C₃₈monovalent hydrocarbon group which may contain a heteroatom. Suitableheteroatoms include oxygen, nitrogen, sulfur and halogen, with oxygenbeing preferred. Of the monovalent hydrocarbon groups, those of 6 to 30carbon atoms are preferred because a high resolution is available infine pattern formation. Suitable monovalent hydrocarbon groups includemethyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl,pentyl, neopentyl, cyclopentyl, hexyl, cyclohexyl, 3-cyclohexenyl,heptyl, 2-ethylhexyl, nonyl, undecyl, tridecyl, pentadecyl, heptadecyl,1-adamantyl, 2-adamantyl, 1-adamantylmethyl, norbornyl, norbornylmethyl,tricyclodecanyl, tetracyclododecanyl, tetracyclododecanylmethyl,dicyclohexylmethyl, icosanyl, allyl, benzyl, diphenylmethyl,tetrahydrofuryl, methoxymethyl, ethoxymethyl, methylthiomethyl,acetamidomethyl, trifluoroethyl, (2-methoxyethoxy)methyl, acetoxymethyl,2-carboxy-1-cyclohexyl, 2-oxopropyl, 4-oxo-1-adamantyl, and3-oxocyclohexyl. Also included are the foregoing groups in which atleast one hydrogen is replaced by a radical containing a heteroatom suchas oxygen, sulfur, nitrogen or halogen, or in which a radical containinga heteroatom such as oxygen, sulfur or nitrogen intervenes betweencarbon atoms, so that the group may contain a hydroxyl, cyano, carbonyl,ether, ester, sulfonic acid ester, carbonate, lactone ring, sultonering, carboxylic acid anhydride or haloalkyl radical.

With respect to the synthesis of the sulfonium salt having an anion offormula (1A′), reference is made to JP-A 2007-145797, JP-A 2008-106045,JP-A 2009-007327, and JP-A 2009-258695. Also useful are the sulfoniumsalts described in JP-A 2010-215608, JP-A 2012-041320, JP-A 2012-106986,and JP-A 2012-153644.

Examples of the sulfonium salt having an anion of formula (1A) are shownbelow, but not limited thereto.

In formula (1B), R^(fb1) and R^(fb2) are each independently fluorine ora straight, branched or cyclic C₁-C₄₀ monovalent hydrocarbon group whichmay contain a heteroatom. Suitable monovalent hydrocarbon groups are asexemplified above for R¹⁰⁵. Preferably R^(fb1) and R^(fb2) each arefluorine or a straight C₁-C₄ fluorinated alkyl group. A pair of R^(fb1)and R^(fb2) may bond together to form a ring with the linkage(—CF₂—SO₂—N—SO₂—CF₂—) to which they are attached, and preferably thepair is a fluorinated ethylene or fluorinated propylene group.

In formula (1C), R^(fc1), R^(fc2) and R^(fc3) are each independentlyfluorine or a straight, branched or cyclic C₁-C₄₀ monovalent hydrocarbongroup which may contain a heteroatom. Suitable monovalent hydrocarbongroups are as exemplified above for R¹⁰⁵. Preferably R^(fc1), R^(fc2)and R^(fc3) each are fluorine or a straight C₁-C₄ fluorinated alkylgroup. A pair of R^(fc1) and R^(fc2) may bond together to form a ringwith the the linkage (—CF₂—SO₂—C—SO₂—CF₂—) to which they are attached,and preferably the pair is a fluorinated ethylene or fluorinatedpropylene group.

In formula (1D), R^(fd) is a straight, branched or cyclic C₁-C₄₀monovalent hydrocarbon group which may contain a heteroatom. Suitablemonovalent hydrocarbon groups are as exemplified above for R¹⁰⁵.

With respect to the synthesis of the sulfonium salt having an anion offormula (1D), reference is made to JP-A 2010-215608 and JP-A2014-133723.

Examples of the sulfonium salt having an anion of formula (1D) are shownbelow, but not limited thereto.

The compound having the anion of formula (1D) has a sufficient acidstrength to cleave acid labile groups in the base polymer because it isfree of fluorine at α-position of sulfo group, but has twotrifluoromethyl groups at β-position. Thus the compound is a useful PAG.

In formula (2), R²⁰¹ and R²⁰² are each independently a straight,branched or cyclic C₁-C₃₀ monovalent hydrocarbon group which may containa heteroatom. R²⁰³ is a straight, branched or cyclic C₁-C₃₀ divalenthydrocarbon group which may contain a heteroatom. Any two of R²⁰¹, R²⁰²and R²⁰³ may bond together to form a ring with the sulfur atom to whichthey are attached. L^(A) is a single bond, ether group, or a straight,branched or cyclic C₁-C₂₀ divalent hydrocarbon group which may contain aheteroatom. X^(A), X^(B), X^(C) and X^(D) are each independentlyhydrogen, fluorine or trifluoromethyl, with the proviso that at leastone of X^(A), X^(B), X^(C) and X^(D) is fluorine or trifluoromethyl, andk is an integer of 0 to 3.

Suitable monovalent hydrocarbon groups include methyl, ethyl, propyl,isopropyl, n-butyl, s-butyl, t-butyl, n-pentyl, t-pentyl, n-hexyl,n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, 2-ethylhexyl,cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl,cyclohexylethyl, cyclohexylbutyl, norbornyl, oxanorbornyl,tricyclo[5.2.1.0^(2,6)]decanyl, adamantyl, phenyl, naphthyl andanthracenyl. Also included are the foregoing groups in which at leastone hydrogen is replaced by a heteroatom such as oxygen, sulfur,nitrogen or halogen, or in which at least one carbon is replaced by aradical containing a heteroatom such as oxygen, sulfur or nitrogen, sothat the group may contain a hydroxyl, cyano, carbonyl, ether bond,ester bond, sulfonic acid ester bond, carbonate bond, lactone ring,sultone ring, carboxylic acid anhydride or haloalkyl radical.

Suitable divalent hydrocarbon groups include linear alkane diyl groupssuch as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl,pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl,nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl,dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl,pentadecane-1,15-diyl, hexadecane-1,16-diyl, heptadecane-1,17-diyl;saturated cyclic divalent hydrocarbon groups such as cyclopentanediyl,cyclohexanediyl, norbornanediyl, and adamantanediyl; and unsaturatedcyclic divalent hydrocarbon groups such as phenylene and naphthylene.Also included are the foregoing groups in which at least one hydrogenatom is replaced by an alkyl group such as methyl, ethyl, propyl,n-butyl or t-butyl, or in which at least one hydrogen atom is replacedby a radical containing a heteroatom such as oxygen, sulfur, nitrogen orhalogen, or in which a radical containing a heteroatom such as oxygen,sulfur or nitrogen intervenes between carbon atoms, so that the groupmay contain a hydroxyl, cyano, carbonyl, ether, ester, sulfonic acidester, carbonate, lactone ring, sultone ring, carboxylic acid anhydrideor haloalkyl radical. Suitable heteroatoms include oxygen, nitrogen,sulfur and halogen, with oxygen being preferred.

Of the PAGs having formula (2), those having formula (2′) are preferred.

In formula (2′), L^(A) is as defined above. R is hydrogen ortrifluoromethyl, preferably trifluoromethyl. R³⁰¹, R³⁰² and R³⁰³ areeach independently hydrogen or a straight, branched or cyclic C₁-C₂₀monovalent hydrocarbon group which may contain a heteroatom. Suitablemonovalent hydrocarbon groups are as exemplified above for R¹⁰⁵. Thesubscripts x and y each are an integer of 0 to 5, and z is an integer of0 to 4.

Examples of the PAG having formula (2) are shown below, but not limitedthereto. Herein R is as defined above.

Of the foregoing PAGs, those compounds having an anion of formula (1A′)or (1D) are especially preferred because of reduced acid diffusion andhigh solubility in resist solvent, and those compounds having an anionof formula (2′) are especially preferred because of minimized aciddiffusion.

An appropriate amount of the acid generator added is 0:1 to 50 parts,more preferably 1 to 40 parts by weight per 100 parts by weight of thebase polymer.

Other Components

With the phthalein alkali metal salt, base polymer, and acid generator,defined above, other components such as an organic solvent, surfactant,dissolution inhibitor, and crosslinker may be blended in any desiredcombination to formulate a chemically amplified positive or negativeresist composition. This positive or negative resist composition has avery high sensitivity in that the dissolution rate in developer of thebase polymer in exposed areas is accelerated by catalytic reaction. Inaddition, the resist film has a high is dissolution contrast,resolution, exposure latitude, and process adaptability, and provides agood pattern profile after exposure, and minimal proximity bias becauseof restrained acid diffusion. By virtue of these advantages, thecomposition is fully useful in commercial application and suited as apattern-forming material for the fabrication of VLSIs. Particularly whena chemically amplified positive resist composition capable of utilizingacid catalyzed reaction is formulated, the composition has a highersensitivity and is further improved in the properties described above.

In the case of positive resist compositions, inclusion of a dissolutioninhibitor may lead to an increased difference in dissolution ratebetween exposed and unexposed areas and a further improvement inresolution. In the case of negative resist compositions, a negativepattern may be formed by adding a crosslinker to reduce the dissolutionrate of exposed area.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144]-[0145] (U.S. Pat. No. 7,537,880).Exemplary solvents include ketones such as cyclohexanone, cyclopentanoneand methyl-2-n-pentyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether; esters such as propylene glycolmonomethyl ether acetate (PGMEA), propylene glycol monoethyl etheracetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, t-butyl acetate, t-butylpropionate, and propylene glycol mono-t-butyl ether acetate; andlactones such as γ-butyrolactone, which may be used alone or inadmixture.

The organic solvent is preferably added in an amount of 100 to 10,000parts, and more preferably 200 to 8,000 parts by weight per 100 parts byweight of the base polymer.

Exemplary surfactants are described in JP-A 2008-111103, paragraphs[0165]-[0166]. Inclusion of a surfactant may improve or control thecoating characteristics of the resist composition. The surfactant ispreferably added in an amount of 0.0001 to 10 parts by weight per 100parts by weight of the base polymer.

The dissolution inhibitor which can be used herein is a compound havingat least two phenolic hydroxyl groups on the molecule, in which anaverage of from 0 to 100 mol % of all the hydrogen atoms on the phenolichydroxyl groups are replaced by acid labile groups or a compound havingat least one carboxyl group on the molecule, in which an average of 50to 100 mol % of all the hydrogen atoms on the carboxyl groups arereplaced by acid labile groups, both the compounds having a molecularweight of 100 to 1,000, and preferably 150 to 800. Typical are bisphenolA, trisphenol, phenolphthalein, cresol novolac, naphthalenecarboxylicacid, adamantanecarboxylic acid, and cholic acid derivatives in whichthe hydrogen atom on the hydroxyl or carboxyl group is replaced by anacid labile group, as described in U.S. Pat. No. 7,771,914 (JP-A2008-122932, paragraphs [0155]-[0178]).

In the positive resist composition, the dissolution inhibitor ispreferably added in an amount of 0 to 50 parts, more preferably 5 to 40parts by weight per 100 parts by weight of the base polymer.

Suitable crosslinkers which can be used herein include epoxy compounds,melamine compounds, guanamine compounds, glycoluril compounds and ureacompounds having substituted thereon at least one group selected fromamong methylol, alkoxymethyl and acyloxymethyl groups, isocyanatecompounds, azide compounds, and compounds having a double bond such asan alkenyl ether group. These compounds may be used as an additive orintroduced into a polymer side chain as a pendant. Hydroxy-containingcompounds may also be used as the crosslinker.

Of the foregoing crosslinkers, examples of suitable epoxy compoundsinclude tris(2,3-epoxypropyl) isocyanurate, trimethylolmethanetriglycidyl ether, trimethylolpropane triglycidyl ether, andtriethylolethane triglycidyl ether. Examples of the melamine compoundinclude hexamethylol melamine, hexamethoxymethyl melamine, hexamethylolmelamine compounds having 1 to 6 methylol groups methoxymethylated andmixtures thereof, hexamethoxyethyl melamine, hexaacyloxymethyl melamine,hexamethylol melamine compounds having 1 to 6 methylol groupsacyloxymethylated and mixtures thereof. Examples of the guanaminecompound include tetramethylol guanamine, tetramethoxymethyl guanamine,tetramethylol guanamine compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, tetramethoxyethyl guanamine,tetraacyloxyguanamine, tetramethylol guanamine compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theglycoluril compound include tetramethylol glycoluril,tetramethoxyglycoluril, tetramethoxymethyl glycoluril, tetramethylolglycoluril compounds having 1 to 4 methylol groups methoxymethylated andmixtures thereof, tetramethylol glycoluril compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theurea compound include tetramethylol urea, tetramethoxymethyl urea,tetramethylol urea compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, and tetramethoxyethyl urea.

Suitable isocyanate compounds include tolylene diisocyanate,diphenylmethane diisocyanate, hexamethylene diisocyanate and cyclohexanediisocyanate. Suitable azide compounds include1,1′-biphenyl-4,4′-bisazide, 4,4′-methylidenebisazide, and4,4′-oxybisazide. Examples of the alkenyl ether group-containingcompound include ethylene glycol divinyl ether, triethylene glycoldivinyl ether, 1,2-propanediol divinyl ether, 1,4-butanediol divinylether, tetramethylene glycol divinyl ether, neopentyl glycol divinylether, trimethylol propane trivinyl ether, hexanediol divinyl ether,1,4-cyclohexanediol divinyl ether, pentaerythritol trivinyl ether,pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitolpentavinyl ether, and trimethylol propane trivinyl ether.

In the negative resist composition, the crosslinker is preferably addedin an amount of 0.1 to 50 parts, more preferably 1 to 40 parts by weightper 100 parts by weight of the base polymer.

In the resist composition of the invention, a quencher other than thephthalein alkali metal salt may be blended. The other quencher istypically selected from conventional basic compounds. Conventional basiccompounds include primary, secondary, and tertiary aliphatic amines,mixed amines, aromatic amines, heterocyclic amines, nitrogen-containingcompounds with carboxyl group, nitrogen-containing compounds withsulfonyl group, nitrogen-containing compounds with hydroxyl group,nitrogen-containing compounds with hydroxyphenyl group, alcoholicnitrogen-containing compounds, amide derivatives, imide derivatives, andcarbamate derivatives. Also included are primary, secondary, andtertiary amine compounds, specifically amine compounds having ahydroxyl, ether, ester, lactone ring, cyano, or sulfonic acid estergroup as described in JP-A 2008-111103, paragraphs [0146]-[0164], andcompounds having a carbamate group as described in JP 3790649. Additionof a basic compound may be effective for further suppressing thediffusion rate of acid in the resist film or correcting the patternprofile.

Quenchers of polymer type as described in U.S. Pat. No. 7,598,016 (JP-A2008-239918) are also useful as the other quencher. The polymericquencher segregates at the resist surface after coating and thusenhances the rectangularity of resist pattern. When a protective film isapplied as is often the case in the immersion lithography, the polymericquencher is also effective for preventing a film thickness loss ofresist pattern or rounding of pattern top.

The other quencher is preferably added in an amount of 0 to 5 parts,more preferably 0 to 4 parts by weight per 100 parts by weight of thebase polymer.

To the resist composition, a polymeric additive (or water repellencyimprover) may also be added for improving the water repellency onsurface of a resist film as spin coated. The water repellency improvermay be used in the topcoatless immersion lithography. Suitable waterrepellency improvers include polymers having a fluoroalkyl group andpolymers having a specific structure with a1,1,1,3,3,3-hexafluoro-2-propanol residue and are described in JP-A2007-297590 and JP-A 2008-111103, for example. The water repellencyimprover to be added to the resist composition should be soluble in theorganic solvent as the developer. The water repellency improver ofspecific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue iswell soluble in the developer. A polymer having an amino group or aminesalt copolymerized as recurring units may serve as the water repellentadditive and is effective for preventing evaporation of acid during PEB,thus preventing any hole pattern opening failure after development. Anappropriate amount of the water repellency improver is 0 to 20 parts,preferably 0.5 to 10 parts by weight per 100 parts by weight of the basepolymer.

Also, an acetylene alcohol may be blended in the resist composition.Suitable acetylene alcohols are described in JP-A 2008-122932,paragraphs [0179][0182]. An appropriate amount of the acetylene alcoholblended is 0 to 5 parts by weight per 100 parts by weight of the basepolymer.

Process

The resist composition is used in the fabrication of various integratedcircuits. Pattern formation using the resist composition may beperformed by well-known lithography processes. The process generallyinvolves coating, prebaking, exposure, and development. If necessary,any additional steps such as PEB may be added.

For example, the positive resist composition is first applied onto asubstrate on which an integrated circuit is to be formed (e.g., Si,SiO₂, SiN, SiON, TiN, WSi, BPSG, SOG, or organic antireflective coating)or a substrate on which a mask circuit is to be formed (e.g., Cr, CrO,CrON, MoSi₂, or SiO₂) by a suitable coating technique such as spincoating, roll coating, flow coating, dipping, spraying or doctorcoating. The coating is prebaked on a hotplate at a temperature of 60 to150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30seconds to 20 minutes. The resulting resist film is generally 0.1 to 2μm thick.

The resist film is then exposed to a desired pattern of high-energyradiation such as UV, deep-UV, EB, EUV, x-ray, soft x-ray, excimer laserlight, γ-ray or synchrotron radiation, directly or through a mask. Theexposure dose is preferably about 1 to 200 mJ/cm², more preferably about10 to 100 mJ/cm², or about 0.1 to 100 μC/cm², more preferably about 0.5to 50 μC/cm². The resist film is further baked (PEB) on a hotplate at 60to 150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30seconds to 20 minutes.

Thereafter the resist film is developed with a developer in the form ofan aqueous base solution for 3 seconds to 3 minutes, preferably 5seconds to 2 minutes by conventional techniques such as dip, puddle andspray techniques. A typical developer is a 0.1 to 10 wt %, preferably 2to 5 wt % aqueous solution of tetramethylammonium hydroxide (TMAH),tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide(TPAH), or tetrabutylammonium hydroxide (TBAH). The resist film in theexposed area is dissolved in the developer whereas the resist film inthe unexposed area is not dissolved. In this way, the desired positivepattern is formed on the substrate. Inversely in the case of negativeresist, the exposed area of resist film is insolubilized and theunexposed area is dissolved in the developer. It is appreciated that theresist composition of the invention is best suited for micro-patterningusing such high-energy radiation as KrF and ArF excimer laser, EB, EUV,x-ray, soft x-ray, γ-ray and synchrotron radiation.

In an alternative embodiment, a negative pattern may be formed viaorganic solvent development using a positive resist compositioncomprising a base polymer having an acid labile group. The developerused herein is preferably selected from among 2-octanone, 2-nonanone,2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone,diisobutyl ketone, methylcyclohexanone, acetophenone,methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate,pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate,butyl formate, isobutyl formate, pentyl formate, isopentyl format;methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate,methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyllactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate,pentyl lactate, isopentyl lactate, methyl 2-hydroxyisobutyrate, ethyl2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, phenyl acetate,benzyl acetate, methyl phenylacetate, benzyl formate, phenylethylformat; methyl 3-phenylpropionate, benzyl propionate, ethylphenylacetate, and 2-phenylethyl acetate, and mixtures thereof.

At the end of development, the resist film is rinsed. As the rinsingliquid, a solvent which is miscible with the developer and does notdissolve the resist film is preferred. Suitable solvents includealcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbonatoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, t-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, t-pentyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-s-butyl ether,di-n-pentyl ether, diisopentyl ether, di-s-pentyl ether, di-t-pentylether, and di-n-hexyl ether. Suitable alkanes of 6 to 12 carbon atomsinclude hexane, heptane, octane, nonane, decane, undecane, dodecane,methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable aromatic solvents includetoluene, xylene, ethylbenzene, isopropylbenzene, t-butylbenzene andmesitylene. The solvents may be used alone or in admixture.

Rinsing is effective for minimizing the risks of resist pattern collapseand defect formation. However, rinsing is not essential. If rinsing isomitted, the amount of solvent used may be reduced.

A hole or trench pattern after development may be shrunk by the thermalflow, RELACS® or DSA process. A hole pattern is shrunk by coating ashrink agent thereto, and baking such that the shrink agent may undergocrosslinking at the resist surface as a result of the acid catalystdiffusing from the resist layer during bake, and the shrink agent mayattach to the sidewall of the hole pattern. The bake is preferably at atemperature of 70 to 180° C., more preferably 80 to 170° C., for a timeof 10 to 300 seconds. The extra shrink agent is stripped and the holepattern is shrunk.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. The abbreviation “pbw” is parts by weight.

Quenchers 1 to 8 in the form of a phthalein alkali metal salt having thefollowing structure were used in resist compositions. Quenchers 1 to 8were prepared by mixing tetraiodophenolphthalein,tetraiodophenolsulfonphthalein, tetraiodofluorescein or derivativeproviding the following anion with an alkali metal hydroxide.

Synthesis Example

Synthesis of Base Polymers (Polymers 1 to 3)

Base polymers were prepared by combining suitable monomers, effectingcopolymerization reaction thereof in tetrahydrofuran (THF) solvent,pouring the reaction solution into methanol for crystallization,repeatedly washing with hexane, isolation, and drying. The resultingpolymers, designated Polymers 1 to 3, were analyzed for composition by¹H-NMR spectroscopy, and for Mw and Mw/Mn by GPC versus polystyrenestandards using THF solvent.

Examples and Comparative Examples

Resist compositions were prepared by dissolving the polymer and selectedcomponents in a solvent in accordance with the recipe shown in Tables 1and 2, and filtering through a filter having a pore size of 0.2 μm. Thesolvent contained 100 ppm of surfactant FC-4430 (3M). The components inTables 1 and 2 are as identified below.

Polymers 1 to 3: identified above

Organic solvents: PGMEA (propylene glycol monomethyl ether acetate)

-   -   CyH (cyclohexanone)    -   PGME (propylene glycol monomethyl ether)

Acid generators: PAG 1 and PAG 2 of the following structural formulae

Comparative Quenchers 1 to 6:

Comparative Additive 1:

EB Lithography Patterning Test

Each of the resist compositions (Tables 1 and 2) was spin coated onto asilicon substrate (which had been vapor primed withhexamethyldisilazane) and prebaked on a hotplate at 110° C. for 60seconds to form a resist film of 80 nm thick. Using a system HL-800D(Hitachi Ltd.) at an accelerating voltage of 50 kV, the resist film wasexposed imagewise to EB in a vacuum chamber. Immediately after theexposure, the resist film was baked (PEB) on a hotplate at thetemperature shown in Tables 1 and 2 for 60 seconds and developed in a2.38 wt % TMAH aqueous solution for 30 seconds to form a pattern.

The resist pattern was evaluated as follows. In the case of positiveresist film, the resolution is a minimum trench size at the exposuredose that provides a resolution as designed of a 120-nm trench pattern.In the case of negative resist film, the resolution is a minimumisolated line size at the exposure dose that provides a resolution asdesigned of a 120-nm isolated line pattern. In the case of positiveresist film, the sensitivity is the exposure dose that provides aresolution to the 120 nm trench pattern. In the case of negative resistfilm, the sensitivity is the exposure dose that provides a resolution tothe 120 nm isolated line pattern. The pattern was observed under SEM todetermine LWR. It is noted that Examples 1 to 9 and Comparative Examples1 to 8 are positive resist compositions, and Example 10 and ComparativeExample 9 are negative resist compositions.

The results are shown in Tables 1 and 2.

TABLE 1 Polymer Acid generator/ Quencher Organic solvent PEB SensitivityLWR Resolution (pbw) additive (pbw) (pbw) (pbw) (° C.) (μC/cm²) (nm)(nm) Example 1 Polymer 1 — Quencher 1 PGMEA (400) 80 35 4.8 75 (100)(3.80) CyH (2,000) PGME (100) 2 Polymer 1 — Quencher 2 PGMEA (400) 80 364.6 75 (100) (3.80) CyH (2,000) PGME (100) 3 Polymer 1 — Quencher 3PGMEA (400) 80 37 4.5 75 (100) (3.90) CyH (2,000) PGME (100) 4 Polymer 1— Quencher 4 PGMEA (400) 80 37 4.2 75 (100) (3.80) CyH (2,000) PGME(100) 5 Polymer 1 — Quencher 5 PGMEA (400) 80 38 4.3 75 (100) (3.80) CyH(2,000) PGME (100) 6 Polymer 1 — Quencher 6 PGMEA (400) 80 37 4.8 75(100) (3.90) CyH (2,000) PGME (100) 7 Polymer 1 — Quencher 1 PGMEA (400)80 36 4.5 75 (100) (1.20) CyH (2,000) Quencher 7 PGME (100) (2.60) 8Polymer 1 — Quencher 8 PGMEA (400) 80 36 4.0 75 (100) (3.90) CyH (2,000)PGME (100) 9 Polymer 2 PAG 2 Quencher 8 PGMEA (2,000) 90 39 5.8 80 (100)(10) (3.80) CyH (500) 10 Polymer 3 PAG 1 Quencher 8 PGMEA (2,000) .10050 6.5 80 (100) (10) (3.80) CyH (500)

TABLE 2 Polymer Acid generator/ Quencher Organic solvent PEB SensitivityLWR Resolution (pbw) additive (pbw) (pbw) (pbw) (° C.) (μC/cm²) (nm)(nm) Comparative 1 Polymer 1 — Comparative PGMEA (400) 80 52 5.7 85Example (100) Quencher 1 CyII (2,000) (2.50) PGME (100) 2 Polymer 1 —Comparative PGMEA (400) 80 56 5.8 85 (100) Quencher 2 CyH (2,000) (2.50)PGME (100) 3 Polymer 1 — Comparative PGMEA (400) 80 50 4.6 80 (100)Quencher 3 CyH (2,000) (3.50) PGME (100) 4 Polymer 1 — Comparative PGMEA(400) 80 52 4.9 80 (100) Quencher 4 CyH (2,000) (3.50) PGME (100) 5Polymer 1 — Comparative PGMEA (400) 80 64 4.6 80 (100) Quencher 5 CyH(2,000) (2.50) PGME (100) 6 Polymer 1 — Comparative PGMEA (400) 80 544.8 80 (100) Quencher 6 CyH (2,000) (3.50) PGME (100) 7 Polymer 1Comparative Comparative PGMEA (400) 80 33 8.5 100 (100) Additive 1Quencher 1 CyH (2,000) (5.0) (3.50) PGME (100) 8 Polymer 2 PAG 2Comparative PGMEA (2,000) 90 48 7.5 85 (100) (10) Quencher 1 CyH (500)(3.50) 9 Polymer 3 PAG 1 Comparative PGMEA (2,000) 100 65 8.0 90 (100)(10) Quencher 1 CyH (500) (3.50)

It is demonstrated in Tables 1 and 2 that resist compositions comprisingalkali metal salts of tetraiodophenolphthalein,tetraiodophenolsulfonphthalein, tetraiodofluorescein, and derivativesform patterns having a high sensitivity, satisfactory resolution, andminimal LWR.

Japanese Patent Application No. 2016-182952 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A resist composition comprising: a basepolymer, an alkali metal salt of a compound selected from the groupconsisting of tetraiodophenolphthalein, tetraiodophenolsulfonphthalein,tetraiodofluorescein, and derivatives thereof, and an organic solvent.2. The resist composition of claim 1 wherein the alkali metal salt hasthe formula (A)-1 or (A)-2:

wherein R¹ and R² are hydrogen, or R¹ and R² may bond together to forman ether group, R³ is hydrogen, halogen, hydroxyl or C₁-C₄ alkoxy group,G is carbonyl or sulfonyl, and A⁺ is an alkali metal ion selected fromthe group consisting of sodium, potassium, rubidium, and cesium ions. 3.The resist composition of claim 1, further comprising an acid generatorcapable of generating sulfonic acid, sulfonimide or sulfonmethide. 4.The resist composition of claim 1, wherein the organic solvent is atleast one selected from the group consisting of a ketone, an ether, anester, and a lactone, and wherein an amount of the organic solvent n theresist composition is from 100 to 10,000 parts by weight per 100 partsby weight of the base polymer.
 5. The resist composition of claim 1wherein the base polymer comprises recurring units having the formula(a1) or recurring units having the formula (a2):

wherein R^(A) is each independently hydrogen or methyl, R¹¹ and R¹² areeach independently an acid labile group, X is a single bond, phenylene,naphthylene, or a C₁-C₁₂ linking group containing ester moiety orlactone ring, and Y is a single bond or ester group.
 6. The resistcomposition of claim 5, further comprising a dissolution inhibitor. 7.The resist composition of claim 5 which is a chemically amplifiedpositive resist composition.
 8. The resist composition of claim 1wherein the base polymer is an acid labile group-free polymer.
 9. Theresist composition of claim 8, further comprising a crosslinker.
 10. Theresist composition of claim 8 which is a chemically amplified negativeresist composition.
 11. The resist composition of claim 1 wherein thebase polymer comprises recurring units of at least one type selectedfrom recurring units having the formulae (f1) to (f3):

wherein R^(A) is each independently hydrogen or methyl, Z¹ is a singlebond, phenylene, —O—Z¹¹—, or —C(═O)—Z¹²-Z¹¹—, Z¹¹ is a straight,branched or cyclic C₁-C₆ alkylene group or straight, branched or cyclicC₂-C₆ alkenylene group which may contain a carbonyl, ester, ether orhydroxyl moiety, or phenylene group, Z¹² is —O— or —NH—, R²¹, R²², R²³,R²⁴, R²⁵, R²⁶, R²⁷, and R²⁸ are each independently a straight, branchedor cyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester orether moiety, or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or mercaptophenyl group,Z² is a single bond, —Z²¹—C(═O)—O—, —Z²¹—O—, or —Z²¹—O—C(═O)—, Z²¹ is astraight, branched or cyclic C₁-C₁₂ alkylene group which may contain acarbonyl, ester or ether moiety, Z³ is a single bond, methylene,ethylene, phenylene, fluorinated phenylene, —O—Z³¹—, or —C(═O)—Z³²—Z³¹—,Z³¹ is a straight, branched or cyclic C₁-C₆ alkylene group or straight,branched or cyclic C₂-C₆ alkenylene group which may contain a carbonyl,ester, ether or hydroxyl moiety, or a phenylene, fluorinated phenyleneor trifluoromethyl-substituted phenylene group, Z³² is —O— or —NH—, A¹is hydrogen or trifluoromethyl, and M⁻ is a non-nucleophilic counterion.
 12. The resist composition of claim 1, further comprising asurfactant.
 13. A pattern forming process comprising the steps ofcoating the resist composition of claim 1 onto a substrate, baking,exposing the resulting resist film to high-energy radiation, anddeveloping with a developer.
 14. The process of claim 13 wherein thehigh-energy radiation is ArF excimer laser of wavelength 193 nm or KrFexcimer laser of wavelength 248 nm.
 15. The process of claim 13 whereinthe high-energy radiation is EB or EUV of wavelength 3 to 15 nm.